Derivational morphology is a type of word formation that creates new lexemes, either by changing syntactic category or by adding substantial new meaning (or both) to a free or bound base. Derivation may be contrasted with inflection on the one hand or with compounding on the other. The distinctions between derivation and inflection and between derivation and compounding, however, are not always clear-cut. New words may be derived by a variety of formal means including affixation, reduplication, internal modification of various sorts, subtraction, and conversion. Affixation is best attested cross-linguistically, especially prefixation and suffixation. Reduplication is also widely found, with various internal changes like ablaut and root and pattern derivation less common. Derived words may fit into a number of semantic categories. For nouns, event and result, personal and participant, collective and abstract noun are frequent. For verbs, causative and applicative categories are well-attested, as are relational and qualitative derivations for adjectives. Languages frequently also have ways of deriving negatives, relational words, and evaluatives. Most languages have derivation of some sort, although there are languages that rely more heavily on compounding than on derivation to build their lexical stock. A number of topics have dominated the theoretical literature on derivation, including productivity (the extent to which new words can be created with a given affix or morphological process), the principles that determine the ordering of affixes, and the place of derivational morphology with respect to other components of the grammar. The study of derivation has also been important in a number of psycholinguistic debates concerning the perception and production of language.
Due to the agglutinative character, Japanese and Ryukyuan morphology is predominantly concatenative, applying to garden-variety word formation processes such as compounding, prefixation, suffixation, and inflection, though nonconcatenative morphology like clipping, blending, and reduplication is also available and sometimes interacts with concatenative word formation. The formal simplicity of the principal morphological devices is counterbalanced by their complex interaction with syntax and semantics as well as by the intricate interactions of four lexical strata (native, Sino-Japanese, foreign, and mimetic) with particular morphological processes. A wealth of phenomena is adduced that pertain to central issues in theories of morphology, such as the demarcation between words and phrases; the feasibility of the lexical integrity principle; the controversy over lexicalism and syntacticism; the distinction of morpheme-based and word-based morphology; the effects of the stage-level vs. individual-level distinction on the applicability of morphological rules; the interface of morphology, syntax, and semantics, and pragmatics; and the role of conjugation and inflection in predicate agglutination. In particular, the formation of compound and complex verbs/adjectives takes place in both lexical and syntactic structures, and the compound and complex predicates thus formed are further followed in syntax by suffixal predicates representing grammatical categories like causative, passive, negation, and politeness as well as inflections of tense and mood to form a long chain of predicate complexes. In addition, an array of morphological objects—bound root, word, clitic, nonindependent word or fuzoku-go, and (for Japanese) word plus—participate productively in word formation. The close association of morphology and syntax in Japonic languages thus demonstrates that morphological processes are spread over lexical and syntactic structures, whereas words are equipped with the distinct property of morphological integrity, which distinguishes them from syntactic phrases.